Debugging projects with multiple processes

I have project which includes at least 3 processes.
And I need to debug child processes.

So first started process initiates others this way:
QProcess *process = new QProcess(this);
...
process->start(PlBinaryFullPath);

Now in QtCreator I can debug only first started process. So if I put breakpoint in the code which is a part of first process, debugger stops on it.
But if I put breakpoint in the code of other process (and it definetly executed), debugger doesn't stop on it.
I have tried to set 'Debug all children' property in QtCreator Tools - Options - Debugger - GDB Extended and have experimented with GDB Additional Startup Commands, but it doesn't help.
Now I've reached only debugging in a such way:

• start project debugging in QtCreator
• open another QtCreator instance and select Debug - Start Debugging - Attach to Running application and choose desired application.
  Nevertheless this way doesn't allow to debug process on startup, for example in main() function, process should been already started.

It will be a very great help if you advise how I can debug child processes in one qtcreator instance and also do it on processes startup.

Note: on Ubuntu setting 'Debug all children' property leads to Debugger doesn't stop on breakpoints even in first process.